Polymer foam projectile-shorting target with hit recorder



p 1968 J. 1.. LA MURA POLYMER FOAM PROJECTILE-SHORTING TARGET WITH HIT RECORDER Filed Oct. 21, 1966 RECORDER PISA F E G.

JOSEPH L. LOMURA INVENTOR ATTORNEY United States Patent "ice POLYMER FOAM PROJECTILE-SHORTING TARGET WITH HET RECORDER Joseph L. La Mura, West Caldwell, N.J., assignor to Joanell Laboratories, Inc., a corporation of New Jersey Filed Oct. 21, 1966, Ser. No. 588,350

Claims. (Cl. 273-1022) This invention relates to a target for electrically recording the perforations caused by small caliber projectiles such as rifle bullets, projectiles from various automatic weapons, and bullets from sub-machine guns. It has specific relationship to a target which is impervious to mois ture and which will withstand repeated perforations by projectiles.

Many targets have been designed and built for training and testing purposes. A large percentage of these targets have been constructed of flimsy materials such as corrugated cardboard, styrene foam, and foam rubber. These targets work well for a few projectiles but they do not last long and a projectile which may strike the target at about the same position as a previous projectile, will not produce a recording pulse. In addition, many of the prior art targets are not waterproof and target practice cannot be held in the rain or in very humid weather.

The present target is designed for use in any weather, including driving rain. The target is made of carefully selected materials which have a zero degree of water absorption and any hole made by a projectile will be closed by the resilient material forming the target laminations and a second projectile through the same spot Will be recorded. The present target is made of an array of layers of plastic foam which contain two metal foil electrodes. The foam layers are cast in such a manner that a continuous impervious layer is on the outside of each target surface so that no moisture can penetrate within the target space.

One of the objects of this invention is to provide an improved target which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to provide a flexible target but having suflicient mechanical strength to withstand the impact of high velocity bullets without tearing or cracking.

Another object of the invention is to provide a target which is impervious to moisture and which can be used in the rain.

Another object of the invention is to provide a target which heals or normalizes itself after each penetration by a projectile.

Another object of the invention is to close the holes formed by projectiles so that no water may enter the target space to register a conductive action.

The invention includes a target for electrically reporting perforations by small caliber projectiles. The target is made of three panels of propylene polymer foam including two layers of metal foil, the five layers being bonded to each other to form a sandwich by a bonding cement.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

FIG. 1 is a front view of the target.

FIG. 2 is a cross sectional view of a portion of the target showing the laminated construction.

:FIG. 3 is a cross sectional view similar to FIG. 2 but showing a projectile piercing the target.

FIG. 4 is one form of circuit which may be used in conjunction with the target.

Referring now to FIG. 1, the target comprises a laminated array 10 of five layers. The details of the construc- 3,401,939 Patented Sept. 17, 1968 tion are shown in FIG. 2 where a front panel 11 is cemented to a sheet of metal foil 12. A central panel 13 is cemented to the other side of foil 12 and also cemented to a second sheet of metal foil 14. The third layer 15 is cemented to the other side of foil 14. It should be noted that the upper end of the target, and also the side edges, have the insulating plastic layers cemented together around the ends of the metal foil so that moisture can be kept away from the conductive elements. The bottom portion of the target 16 is formed in a similar manner but at this edge two conductors 17 and 18 are brought out through the bottom surface for connection to an external circuit.

FIG. 3 shows a cross sectional portion of the target similar to FIG. 2 but having a projectile 20' moving through the target. It should be noted that all five layers of the target are displaced by the projectile in the direction of the projectile motion. The three flexible layers 11, 13, and 15 are also compressed by the penetration of the projectile and, after the projectile has left the target, the three foam layers move back into place and seal the hole. The metal foil layers 12 and 14 are displaced by the projectile and form a connection between the electrodes so that current can pass between them and be recorded by means of an external circuit. There are times when a portion of the first electrode may be drawn into contact with the second electrode to form a shorted connection. The external circuit is arranged so that a large current will then be applied to this short circuit and quickly burn it out to normalize the recorder circuit and condition the target for another projectile action.

The three foam layers 11, 13, and 15 are made of propylene polymer foam which is constructed so that the foam bubbles are very small. One such material which is suitable for this type of target is commercially available under the trade name of Minnicel and sold by the Hercules Powder Company of Bloomington, 'Del. Any good self-setting bonding cement may be used to bond the laminations together. It is preferable to employ a cement which is flexible after setting.

When the above described target is employed for recording hits by projectiles, a coupling circuit is connected between the target and a recorder 21. A preferred circuit is shown in FIG. 4 where the target conductors 17 and 18 are connected to a positive conductor 22 and an indicating lamp 23. A storage battery 19 of about twenty-four volts is connected across conductors 17 and 18. The other side of the indicating lamp 23 is connected to a grounded conductor 24 which is also connected to the negative terminal of a direct current power supply 25. As manually operated switch 26 may be connected in series between the power supply and the ground conductor 24 to disconnect the source of power when the circuit is not being used. The switch is a safety means for insuring that leakage current cannot flow in the circuit. It is not necessary because when there is no current passing through the target, there is no current flowing elsewhere in the circuit.

The coupling circuit includes a controlled rectifier 27 and a unijunction transistor 28. A firing electrode 30 of the controlled rectifier 27 is coupled through a rectifier diode 31 and a capacitor 32 to the junction between conductor 1-8 and one side of lamp 23. This circuit transmits a pulse to the rectifier 27 causing it to conduct and send current from the positive conductor 22 through rectifier and resistor 33, thereby applying a positive potential over conductor 34 to resistor 35 and capacitor 36 to charge capacitor 36. Capacitor 36 reaches its predetermined charging voltage after a short time interval which is determined by the RC charging circuit including resistor 35 and capacitor 36. As the voltage builds up on capacitor 36, the voltage of the emitter of the unijunction transistor 28 is raised until the firing voltage is reached. At this point capacitor 36 discharges its quantity of elec- 3 tricity through the unijunction transistor 28 and resistor 37.

When the controlled rectifier 27 is made conductive, a positive pulse is applied over conductors 34 and 38 to operate recorder 21. The current through the controlled rectifier 27 continues to flow until the unijunction transistor is fired. The time interval between these two events produces a recording pulse which is at least five times longer and may be many times longer than the pulse received from the target 10. When the unijunction transistor 28 transfers the charge from capacitor 36, the potential of conductors 38 and 34 rise because of a positive pulse transmitted through diode 43 and capacitor 40. This action stops conduction through rectifier 27 and the entire circuit is normalized.

The circuit also includes a diode rectifier 41 which is put in the circuit in order to eliminate any voltage pulses which might raise conductors 34 and 38 above the voltage of the power supply 25. If, for any reason, an inductive kick is applied to these conductors, the excess voltage will be transferred to the power supply which will absorb the additional voltage. Another diode 42 is bridged across the recorder terminals to protect the recorder circuit from negative pulses which may be applied to conductor 38. A third diode 43 is connected between the number 1 base of the unijunction transistor 28 and capacitor 40 so that the capacitor 40 cannot discharge through the unijunction transistor elements and resistor 44.

Under ordinary working conditions the current pulse through lamp 23 will not be enough to light the lamp since the pulse is too short. However, if metal film 12 is displaced so that it makes contact with film 14 and the short persists, lamp 23 will be lighted, indicating that the target is temporarily not in a condition to record another projectile. It has been found that a condition such as that described above will persist for less than one second at which time the current from the storage battery 19 will burn out the short circuit and normalize the target. At this time lamp 23 goes out and the circuit is ready for another recording operation.

The target described above includes three laminations of propylene foam polymer which has been cast with minute bubbles to produce the action desired. It is within the provisions of the invention to use other substances which are similar to this plastic foam and have the same mechanical and electrical characteristics. The only limitations of the invention are therefore to be determined from the scope of the appended claims.

I claim:

1. A target for electrically recording the perforations caused by projectiles comprising; a fiat supporting insulator composed of polypropylene foam to form a central flexible panel, an electrode cemented to each side of said insulator, each of said electrodes composed of a metal conducting foil; two additional fiat insulator panels bonded to said electrodes by a cement for waterproofing the target and for increasing its mechanical strength, said additional panels also formed of polypropylene foam, and a recorder circuit coupled to said target electrodes for recording each current pulse caused by a projectile penetrating the two metal foil electrodes.

2. A target as claimed in claim 1 wherein said two foil electrodes are each respectively connected to a conductor for connection to said recorder circuit.

3. A target as claimed in claim 1 wherein said supporting insulator is secured to the electrodes and to the additional insulator panels by means of a self-setting cement which is applied to both sides of the foil electrodes and which is flexible when set.

4. A target as claimed in claim 1 wherein the edges of all the foam layers are cemented together at the edges to seal the metal foil electrodes from ambient conditions.

5. A target and a recorder circuit as claimed in claim 1 wherein a coupling circuit is connected between the target electrodes and the recording circuit, said coupling circuit including a source of direct current power, a controlled rectifier and a unijunctional transistor for converting an applied electrical pulse of short duration into an electrical pulse having a duration of at least five times the duration of the applied pulse.

6. A target and recorder circuit as claimed in claim 5 wherein said source of direct current power is connected in series with an indicating lamp and the electrodes of the target.

7. A target and recorder circuit as claimed in claim 6 wherein the controlled rectifier is connected across the power supply and a firing electrode is connected to the junction point of the indicating lamp and the target for rendering the rectifier conductive each time the target electrodes are connected together.

8. A target and recorder circuit as claimed in claim 6 wherein said unijunction transistor is coupled between the controlled rectifier and the recorder, said unijunction transistor having an emitter electrode, a base 1, and a base 2 electrode, the emitter electrode connected to the cathode of said controlled rectifier in series with a resistor, base 1 electrode also connected to the cathode in series with a resistor, and a base 2 electrode connected to the negative terminal of the power source.

9. A target and recorder circuit as claimed in claim 6 wherein said unijunction transistor includes a base 1 electrode connected to the cathode of said controlled rectifier in series with a diode and a capacitor for turning off the rectifier and making it non-conductive when the unijunction transistor is made conductive.

10. A target and recorder circuit as claimed in claim 6 wherein the recorder circuit includes means to light said indicating lamp whenever a short circuit exists between said target electrodes due to the passage of a projectile through the target.

References Cited UNITED STATES PATENTS 2,576,960 12/1951 McAvoy 273-1022 2,819,084 1/1958 Brown et al 273l02.2 2,819,085 1/1958 Brown et al 273--102.2 3,004,763 10/1961 Knapp 273102.2 3,158,372 11/1964 Ohlund et al 273-102.2 3,215,933 11/1965 Scanlon 273-1022 X FOREIGN PATENTS 1,369,840 7/1964 France.

ANTON O. OECHSLE, Primary Examiner.

M. R. PAGE, Assistant Examiner. 

1. A TARGET FOR ELECTRICALLY RECORDING THE PERFORATIONS CAUSED BY PROJECTILES COMPRISING; A FLAT SUPPORTING INSULATOR COMPOSED OF POLYPROPYLENE FOAM TO FORM A CENTRAL FLEXIBLE PANEL, AN ELECTRODE CEMENTED TO EACH SIDE OF SAID INSULATOR, EACH OF SAID ELECTRODES COMPOSED OF A METAL CONDUCTING FOIL; TWO ADDITIONAL FLAT INSULATOR PANELS BONDED TO SAID ELECTRODES BY A CEMENT FOR WATERPROOFING THE TARGET AND FOR INCREASING ITS MECHANICAL STRENGTH, SAID ADDITIONAL PANELS ALSO FORMED OF POLYPROPYLENE FOAM, AND A RECORDER CIRCUIT COUPLED TO SAID TARGET ELECTRODES FOR RECORDING EACH CURRETN PULSE CAUSED BY A PROJECTILE PENETRATING THE TWO METAL FOIL ELECTRODES. 